1. Field of the Invention
The present invention is related to microwave integrated circuits (MICs) and, more particularly, is directed towards MICs configured as open ring resonators and which use active elements as driving means.
2. Description of the Prior Art
The TRAPATT diode is a high efficiency and high power solid state device which was discovered by H. J. Prager et al in 1967 (Proc. IEEE, Volume 55, pages 586-587).
Since then, it has been analyzed by many researchers, and is now usefully applied in either a pulsed mode or a CW mode. Recently, the TRAPATT diode has found many system applications, such as in phased antenna arrays, radars, and the like. See, for example, M. I. Grace in European Microwave Conference Digest (1961), Stockholm, Sweden, and A. Rosen et al in RCA Review, Volume 33, No. 4 (1972).
The TRAPATT diode oscillator or amplifier circuits, exemplified in the above-cited literature, suffer from several deficiencies. For example, they are often too complex, being either bulky when used with coaxial line, or too inefficient because of excess losses in common linear microstrip circuits.
Additionally, especially for a TRAPATT oscillator, harmonic reactive (i.e., lossless) tuning requirements must be satisfied for TRAPATT mode initiation and reasonably efficient operation; this requires at least up to the fourth harmonic to be considered.
In coaxial circuits, the tuning typically necessitates the use of multi-slugs with selected characteristic impedances and critical spacing, as pointed out by W. J. Evans in IEEE, MTT TRANS., Volume 12, pages 1060-1067 (1969). In a linear microstrip circuit, reactive shunt stubs of selected length and spacing are chosen, as exemplified by the above-cited article by Rosen. Other configurations utilize series and/or shunt circuits that are tuned to frequencies which are harmonically related to the TRAPATT's fundamental frequency.
In addition to the foregoing, TRAPATT circuit combining encounters considerable problems due to requirements of tuning synchronism and efficient and stable operation of the oscillators. This is of particular importance for pulsed operation, where non-synchronous tuning results in frequency jitter. A push-pull circuit arrangement has been suggested by H. Kawamoto, Intern. MTT Symposium (1971), but it requires careful selection of devices and tuning.
de Ronde and Shammas describe "MIC Bandfilters Using Open-Ring Resonators" in Proc. of the Fourth European Microwave Conference, pages 531-535 (1974) which took place in Montreux, France. In this article, the authors minimize radiation and surface wave excitation of microstrip filters by configuring same in a half-wavelength open-ring resonator.